1. Field of the Invention
The present invention generally relates to a LAN signal transmitting method and a transmitting apparatus using the method, and especially relates to a LAN signal transmitting method and a transmitting apparatus using the method wherein the transmission apparatuses are provided between LAN apparatuses so that a LAN signal is transmitted and received.
2. Description of the Related Art
Methods of transmitting LAN (Local Area Network) signals, such as Gigabit Ethernet (registered trademark) signals, a long distance at high speed are proposed. In the present specification, LAN includes MAN (Metropolitan Area Network) and WAN (Wide Area Network).
The conventional methods include
a method of mapping an IP (Internet Protocol) signal to an SDH (Synchronous Digital Hierarchy) frame after accommodating the IP signal in ATM (Asynchronous Transfer Mode), and
a method of accommodating the IP signal in the SDH frame after the IP signal has been once terminated in a higher layer such as the layer 3 of the OSI basic reference model. According to the conventional methods, an intermediary framing process in the case of ATM, and the termination in the higher layer are required. For this reason, overhead (useless processing) becomes a significant burden, and a problem is in that a processing circuit becomes complicated and processing delay becomes significant.
For example, Patent Reference 1 discloses a method of directly mapping LAN signals, such as Gigabit Ethernet (registered trademark) signals, onto an OTN (Optical Transport Network) frame. Here, OTN refers to the transmission frame form of the digital wrapper method recommended by ITU-T G.709.
However, the problem with the method disclosed by Patent Reference 1 is that the transmission efficiency is degraded due to, e.g., vacant bytes that have to be inserted. Patent Reference 2 attempts to solve this problem by raising accommodation efficiency by carrying out 8B/10B decoding of the LAN signals, whereby only a data section of the LAN signals is extracted and mapped onto the OTN frame.
However, the method proposed by Patent Reference 2 has a problem in transmitting the control code that is a part of the LAN signal other than the data section. The control code of the LAN signal is for exchanging status information between adjacent transmission apparatuses. Since the control code is terminated when the 8B/10B decoding is carried out, the control code after decoding has to be accommodated in the OTN frame so that LAN connection between the transmission apparatuses is maintained.
FIG. 1 shows the configuration of common LAN apparatuses 10 and 11 that transmit and receive the LAN signal. Here, although the LAN apparatuses 10 and 11 contain functional blocks L1 through L7 depending on the number of layers that are terminated, a LAN apparatus generally contains up to the layer 2 (MAC layer).
The layer 1 (physical layer) of each of the LAN apparatuses 10 and 11 is called PHY, and performs optical/electrical conversion of the LAN signal, 8B/10B encoding and decoding, management of a link state, etc. Management of the link state is performed by exchanging a control code (C. C.) and a data set for control called configuration register between the PHYs.
The format and information of the control code are shown in FIG. 2, where FD (Full Duplex) and HD (Half Duplex) specify whether full duplex or half-duplex, respectively, is to be performed. The type of the link state, a flow control, etc., are exchanged by PS (Pause), RF (Remote Fault), and ACK (Acknowledge).
The exchange of the control code is called “negotiation”, and if the negotiation is established, the state of the link is called “link up”. Then, the information exchanged here can be provided to a higher layer, and information from the higher layer can be set up.
Where transmission apparatuses 12 and 13 are arranged between the LAN apparatuses 10 and 11 as shown in FIG. 3, the control code has to be exchanged between the LAN apparatuses 10 and 11 through the transmission apparatuses 12 and 13 so that the LAN apparatuses 10 and 11 are linked through the transmission apparatuses 12 and 13.
As shown in FIG. 4, the LAN signal from the LAN apparatus 10 is decoded by an 8B/10B decoding unit of the transmission apparatus 12, where the data and the control code are extracted, the control code is provided to the overhead of SDH by an OHB mapping unit 14, and is provided to the transmission apparatus 13. Then, the transmission apparatus 13 extracts the control code from the overhead of SDH, combines the control code and the data, and encodes the data and the control code by an 8B/10B encoding unit. In this way, the LAN apparatuses 10 and 11 are linked through the transmission apparatuses 12 and 13. This is the conventional method proposed by, e.g., Patent Reference 3.
In addition, Patent Reference 4 discloses transfer processing of an information packet in a WDM (Wavelength Division Multiplexing) communication system. Further, Patent Reference 5 discloses a technique using an alarm mask in an opposite direction in a WDM communication system.
[Patent Reference 1] JPA 2002-217940
[Patent Reference 2] JPA 2001-45069
[Patent Reference 3] JPA 2004-357164
[Patent Reference 4] JPA 2001-111526
[Patent Reference 5] JPA 2002-319909